**3.1 pH of digestate**

Generally, the pH of digestate is alkaline (Table 1). Increases in pH values in the course of the AD may have been caused by the formation of (NH4)2CO3 (Georgacakis et al., 1992).


Table 1. Changes of the pH in different digestion systems

The pH is increased under the digesting process, but its range depends on the quality of ingestate and the digestion process. The end values are irrespective of the starting value.

Two types of digestate are the liquid and the solid ones which are distinguished on the bases of their dry matter (DM) content. The liquid digestate contains less than 15% DM content, while the solid digestate contains more than 15% DM. Solid digestate can be used similar to the composts or could be composted with other organic residues and can be more economically transported over grater distances than the liquid material (Møller et

The quality of a digestate is determined by the digestion process used and the composition of ingestates therefore the agricultural use and efficacy of the nascent materials could be different. Nevertheless, some common rules can be found in the course of the digestion

Generally, the pH of digestate is alkaline (Table 1). Increases in pH values in the course of the AD may have been caused by the formation of (NH4)2CO3 (Georgacakis et al., 1992).

The pH is increased under the digesting process, but its range depends on the quality of ingestate and the digestion process. The end values are irrespective of the starting value.

pH of intermedier stage

solid type digester 7.0 7.5 7.8 *Gómez* 

liquid type digester 6.9 7.2 7.6 *Gómez* 

pH of digestate

3.5 5.0 7.5 *Gómez* 

4.8 7.5 8.7 *Pognani* 

4.0 8.1 8.3 *Pognani* 

Source of data

*et al., 2007*

*et al., 2007*

*et al., 2007*

*et al., 2009* 

*et al., 2009* 

pH of ingestate

process which allow us to evaluate the results of a digestion process.

Type of digestion process

mesophilic,

thermophilic (co-digestion), liquid type digester

thermophilic (co-digestion), liquid type digester

thermophilic (co-digestion), liquid type digester

Table 1. Changes of the pH in different digestion systems

al., 2000).

**3. Composition of digestate** 

**3.1 pH of digestate** 

Type of ingestate

Pharmaceutical industry sludge

Primary sludge from municipal waste water treatment plant and organic fractions of municipal solid wastes

Energy crops, cow manure slurry and agroindustrial waste

Energy crops, cow manure slurry, agroindustrial waste and OFMSW

Cattle manure mesophilic,

The alkaline pH of digestate is a useful property because of the worldwide problem of soil acidification.
